The present invention relates to method for identifying an object and measuring its position and its orientation, and to a device for carrying out the method.
The problem of identifying an object and measuring its position and its orientation arises in many technical arts, for example in designing machines which are capable of automatically assembling the various components of a mechanical, electrical, or other, assembly or sub-assembly. Such machines are often referred to as industrial robots.
Devices for overcoming that problem have already been proposed. French patent application No. 2 405 517 for example describes a device comprising a memory for storing data provided by a television camera directed onto the object to be identified. The data stored in the memory are analysed by electronic means for determining the position of the centroid of the image representing the object, and for producing an electrical signal which is characteristic of the shape of the object. The electrical signal is then compared to a certain number of signals which have been stored during a learning phase and which are characteristic of one of the types of objects which may be presented before the device. The result of the comparison operation makes it possible to identify the object being examined, and to determine its angular position with respect to a reference position.
This device suffers from the disadvantage of being slow, because of the considerable number of data that it is required to process. The distortion phenomena introduced by the television camera may also result in errors of object identification and positional measurement.
Other devices described for example in U.S. Pat. No. 4,207,002 measure the correlation between an image which is representative of the Fourier spectrum of the object being examined and the Fourier spectrum of a reference object which is recorded in the form of a hologram. Good correlation indicates that the object being examined is identical to the reference object. The position of the correlation peak in the measuring plane also gives information relating to the position of the object in question.
In comparison with the first described device, this device has the great advantage of parallel processing of all the data which are representative of the object being examined, and is therefore very quick.
However, this device suffers from the disadvantage of being highly sensitive to the angular position of the object being examined. If that position is not identical to the position of the reference object which was used to produce the hologram, the height or the intensity of the correlation peak is reduced and the peak may even disappear.
This disadvantage can be overcome by means of an accessory device which is described for example in U.S. Pat. No. 4,174,885, which rotates the reference hologram. However, this accessory device seriously complicates the design of the recognition device and reduces its operation speed.
In addition, such device permits recognition of only a single type of object at a time. If a number of types of objects of different shapes are to be recognised, a plurality of devices must be provided, each being equipped with the hologram corresponding to one of those types of object.